# Pastebin CH0Hbfku
prop ::
  forall field f structure inner.
  ( KnownSymbol field,
    HasField' (AppendSymbol "_" field) (HKD structure f) (f (Maybe inner)),
    Applicative f
  ) =>
  inner ->
  HKD structure f ->
  HKD structure f
prop a x = x & field @(AppendSymbol "_" field) .~ pure (Just a)